<p>Cortical potentials evoked by flashes or clicks were studied in the CER situation and found to increase by over 200% when these evoking stimuli served as conditional stimuli (classical conditioning), when neutral flashes were paired with click CS's (compound conditioning), and when flashes followed painful shock (backward conditioning) which sometimes suppressed bar pressing. Similar increases were evoked in other animals during high voltage slow electroencephalographic sleep or drowsiness. Only cortical components (not afferent activity) of the evoked response were found to increase with these different behavioral conditions, but the changes are not attributed to conditioning per se or dependent on immobility.</p>